The invention relates to methods and devices for placing under tension, multiple strand cables such as those constituting stays which serve for supporting bridge decks or for stabilizing towers of great height.
In placing such a cable under tension, which is carried out to anchor the second end of this cable on a suitable block, after anchoring its first end on another block, it is convenient to give identical values to the tensions of the different strands or constituent twists of the cable, which are identical with one another, in order that all these strands may participate uniformly in the traction force of the cable.
Such a result can be obtained by exerting the anchoring tension on the whole of the cable, that is to say simultaneously on all of the strands mounted in parallel.
However, it is then necessary to resort to a particularly heavy and bulky tension jack, which can constitute a major drawback, in particular for uses where the head of the cable to be anchored is difficult of access.
To overcome this drawback, it has been proposed to tighten the strands one by one by means of a small individual jack.
However, it is then difficult to obtain identical values for the tension applied successively to the different strands, since the tensioning of each strand eases slightly the previously tightened strands, which modifies the values of the tensions of the different strands in the course of the complete tensioning of the cable.
The formulae which have been proposed until now to overcome this drawback have not given satisfaction, being manifested particularly by very difficult calculations or by sequences of operations particularly delicate to carry out.